1. Field of the Invention
The present invention relates to a vehicle headlamp in which a vibration resistance is improved by connecting a lamp unit to another member using two connection sections.
2. Related Art
There is a vehicle headlamp in which a lamp unit having a light source is disposed inside a lamp casing formed of a cover and a lamp housing.
As shown in JP-A-2004-227933, the lamp unit of the vehicle headlamp can be subjected to an initial position adjustment (aiming adjustment) of an irradiation direction thereof using an optical axis adjustment mechanism (aiming adjustment mechanism). In this kind of vehicle headlamp, it is possible to carry out a so-called right-left aiming adjustment in which the lamp unit is turned in a right-left direction (horizontal direction) with respect to the lamp casing and a so-called up-down aiming adjustment in which the lamp unit is tilted in an up-down direction with respect to the lamp casing.
In the vehicle headlamp described in JP-A-2004-227933, the lamp unit is supported on a frame passing through in a front-rear direction, and the frame is supported on the lamp housing via two adjustment shafts having screw sections and one fulcrum shaft. Rear end sections of the fulcrum shaft and the two adjustment shafts are connected to the lamp housing, a front end section of the fulcrum shaft is connected to a lower end section of the frame, and front end sections of the two adjustment shafts are connected to an upper end section of the frame while being separated from each other in the right-left direction.
In the vehicle headlamp, when the screw sections are screwed into or out of the frame by rotating the adjustment shafts, the frame and the lamp unit are integrally turned in the horizontal direction or tilted substantially in the up-down direction around the fulcrum shaft, whereby the right-left aiming adjustment or the up-down aiming adjustment is carried out.
In the vehicle headlamp of JP-A-2004-227933, the lamp unit is required to be moved (turned) along a circular arc locus with respect to the lamp housing during the aiming adjustment. In contrast, the locus of the operating point of the lamp unit, i.e., the connection point between the adjustment shaft and the frame, becomes linear. Hence, during the aiming adjustment, a load is generated in the lamp unit in a direction orthogonal to the locus of the operating point. Therefore, it is necessary to make design allowance (play) for absorbing this load.
However, in the case that the lamp unit is structured so as to have the above-mentioned allowance, the lamp unit becomes easy to move by the amount of the allowance, for example, due to vibration occurring during the traveling of a vehicle. As a result, displacement and vibration are apt to easily occur in the lamp unit.
In addition, in the vehicle headlamp of JP-A-2004-227933, since the lamp unit is turnably supported on the lamp housing via three connection points, i.e., the fulcrum shaft connected to the frame and the two adjustment shafts, the three connection points are located at positions away from the gravity center of the lamp unit. Eventually, the positions subjected to vibration become away from the gravity center of the lamp unit.
Furthermore, in the vehicle headlamp of JP-A-2004-227933, the frame for supporting the lamp unit is structured so as to be supported on the lamp housing via the fulcrum shaft and the two adjustment shafts. Hence, since the total load of the lamp unit and the frame is applied to the fulcrum shaft and the two adjustment shafts, vibration resistance at the adjustment shafts, etc. is reduced.